openmp: Eliminate non-matching metadirective variants early in Fortran front-end

This patch checks during parsing if a metadirective selector is both
resolvable and non-matching - if so, it is removed from further
consideration.  This is both more efficient, and avoids spurious
syntax errors caused by considering combinations of selectors that
lead to invalid combinations of OpenMP directives, when that
combination would never arise in the first place.

This exposes another bug - when metadirectives that are not of the
begin-end variety are nested, we might have to drill up through
multiple layers of the state stack to reach the state for the
next statement.  This is now fixed.

2022-02-11  Kwok Cheung Yeung  <kcy@codesourcery.com>

	gcc/
	* omp-general.cc (DELAY_METADIRECTIVES_AFTER_LTO): Check that cfun is
	non-null before derefencing.

	gcc/fortran/
	* decl.cc (gfc_match_end): Search for first previous state that is not
	COMP_OMP_METADIRECTIVE.
	* gfortran.h (gfc_skip_omp_metadirective_clause): Add prototype.
	* openmp.cc (match_omp_metadirective): Skip clause if
	result of gfc_skip_omp_metadirective_clause is true.
	* trans-openmp.cc (gfc_trans_omp_set_selector): Add argument and
	disable	expression conversion if false.
	(gfc_skip_omp_metadirective_clause): New.

	gcc/testsuite/
	* gfortran.dg/gomp/metadirective-8.f90: New.

9 files changed, 101 insertions, 16 deletions

diff --git a/gcc/ChangeLog.omp b/gcc/ChangeLog.omp
index abcdb02..d093c79 100644
--- a/gcc/ChangeLog.omp
+++ b/gcc/ChangeLog.omp
@@ -1,3 +1,8 @@
+2022-02-11  Kwok Cheung Yeung  <kcy@codesourcery.com>
+
+	* omp-general.cc (DELAY_METADIRECTIVES_AFTER_LTO): Check that cfun is
+	non-null before derefencing.
+
 2022-01-28  Kwok Cheung Yeung  <kcy@codesourcery.com>
 
 	* gimplify.cc (gimplify_omp_metadirective): Mark offloadable functions
diff --git a/gcc/fortran/ChangeLog.omp b/gcc/fortran/ChangeLog.omp
index e726220..180a54b 100644
--- a/gcc/fortran/ChangeLog.omp
+++ b/gcc/fortran/ChangeLog.omp
@@ -1,3 +1,14 @@
+2022-02-11  Kwok Cheung Yeung  <kcy@codesourcery.com>
+
+	* decl.cc (gfc_match_end): Search for first previous state that is not
+	COMP_OMP_METADIRECTIVE.
+	* gfortran.h (gfc_skip_omp_metadirective_clause): Add prototype.
+	* openmp.cc (match_omp_metadirective): Skip clause if
+	result of gfc_skip_omp_metadirective_clause is true.
+	* trans-openmp.ccc (gfc_trans_omp_set_selector): Add argument and
+	disable expression conversion if false.
+	(gfc_skip_omp_metadirective_clause): New.
+
 2022-01-25  Kwok Cheung Yeung  <kcy@codesourcery.com>
 
 	* openmp.cc (omp_target_device_selectors): New.
diff --git a/gcc/fortran/decl.cc b/gcc/fortran/decl.cc
index e024e36..a77ac76 100644
--- a/gcc/fortran/decl.cc
+++ b/gcc/fortran/decl.cc
@@ -8325,15 +8325,32 @@ gfc_match_end (gfc_statement *st)
 
     case COMP_CONTAINS:
     case COMP_DERIVED_CONTAINS:
-    case COMP_OMP_METADIRECTIVE:
     case COMP_OMP_BEGIN_METADIRECTIVE:
       state = gfc_state_stack->previous->state;
       block_name = gfc_state_stack->previous->sym == NULL
-		 ? NULL : gfc_state_stack->previous->sym->name;
+		   ? NULL : gfc_state_stack->previous->sym->name;
       abreviated_modproc_decl = gfc_state_stack->previous->sym
 		&& gfc_state_stack->previous->sym->abr_modproc_decl;
       break;
 
+    case COMP_OMP_METADIRECTIVE:
+      {
+	/* Metadirectives can be nested, so we need to drill down to the
+	   first state that is not COMP_OMP_METADIRECTIVE.  */
+	gfc_state_data *state_data = gfc_state_stack;
+
+	do
+	{
+	  state_data = state_data->previous;
+	  state = state_data->state;
+	  block_name = state_data->sym == NULL
+		       ? NULL : state_data->sym->name;
+	  abreviated_modproc_decl = state_data->sym
+		&& state_data->sym->abr_modproc_decl;
+	}
+	while (state == COMP_OMP_METADIRECTIVE);
+      }
+      break;
     default:
       break;
     }
diff --git a/gcc/fortran/gfortran.h b/gcc/fortran/gfortran.h
index d4ad902..edc45ca 100644
--- a/gcc/fortran/gfortran.h
+++ b/gcc/fortran/gfortran.h
@@ -3950,4 +3950,8 @@ bool gfc_is_reallocatable_lhs (gfc_expr *);
 void finish_oacc_declare (gfc_namespace *, gfc_symbol *, bool);
 void gfc_adjust_builtins (void);
 
+/* trans-openmp.c */
+
+bool gfc_skip_omp_metadirective_clause (gfc_omp_metadirective_clause *);
+
 #endif /* GCC_GFORTRAN_H  */
diff --git a/gcc/fortran/openmp.cc b/gcc/fortran/openmp.cc
index 0fc7e64..3661271 100644
--- a/gcc/fortran/openmp.cc
+++ b/gcc/fortran/openmp.cc
@@ -5195,8 +5195,11 @@ match_omp_metadirective (bool begin_p)
 	  new_st.ext.omp_clauses = NULL;
 	}
 
-      *next_clause = omc;
-      next_clause = &omc->next;
+      if (!gfc_skip_omp_metadirective_clause (omc))
+	{
+	  *next_clause = omc;
+	  next_clause = &omc->next;
+	}
     }
 
   if (gfc_match_omp_eos () != MATCH_YES)
diff --git a/gcc/fortran/trans-openmp.cc b/gcc/fortran/trans-openmp.cc
index 1b18e93..a0f2139 100644
--- a/gcc/fortran/trans-openmp.cc
+++ b/gcc/fortran/trans-openmp.cc
@@ -7627,7 +7627,8 @@ gfc_trans_omp_declare_simd (gfc_namespace *ns)
 }
 
 static tree
-gfc_trans_omp_set_selector (gfc_omp_set_selector *gfc_selectors, locus where)
+gfc_trans_omp_set_selector (gfc_omp_set_selector *gfc_selectors, locus where,
+			    bool conv_expr_p = true)
 {
   tree set_selectors = NULL_TREE;
   gfc_omp_set_selector *oss;
@@ -7648,11 +7649,15 @@ gfc_trans_omp_set_selector (gfc_omp_set_selector *gfc_selectors, locus where)
 		case CTX_PROPERTY_USER:
 		case CTX_PROPERTY_EXPR:
 		  {
-		    gfc_se se;
-		    gfc_init_se (&se, NULL);
-		    gfc_conv_expr (&se, otp->expr);
-		    properties = tree_cons (NULL_TREE, se.expr,
-					    properties);
+		    tree expr = NULL_TREE;
+		    if (conv_expr_p)
+		      {
+			gfc_se se;
+			gfc_init_se (&se, NULL);
+			gfc_conv_expr (&se, otp->expr);
+			expr = se.expr;
+		      }
+		    properties = tree_cons (NULL_TREE, expr, properties);
 		  }
 		  break;
 		case CTX_PROPERTY_ID:
@@ -7688,11 +7693,16 @@ gfc_trans_omp_set_selector (gfc_omp_set_selector *gfc_selectors, locus where)
 
 	  if (os->score)
 	    {
-	      gfc_se se;
-	      gfc_init_se (&se, NULL);
-	      gfc_conv_expr (&se, os->score);
+	      tree expr = NULL_TREE;
+	      if (conv_expr_p)
+		{
+		  gfc_se se;
+		  gfc_init_se (&se, NULL);
+		  gfc_conv_expr (&se, os->score);
+		  expr = se.expr;
+		}
 	      properties = tree_cons (get_identifier (" score"),
-				      se.expr, properties);
+				      expr, properties);
 	    }
 
 	  selectors = tree_cons (get_identifier (os->trait_selector_name),
@@ -7883,3 +7893,11 @@ gfc_trans_omp_metadirective (gfc_code *code)
 
   return metadirective_tree;
 }
+
+bool gfc_skip_omp_metadirective_clause (gfc_omp_metadirective_clause *clause)
+{
+  tree selector = gfc_trans_omp_set_selector (clause->selectors,
+					      clause->where, false);
+
+  return omp_context_selector_matches (selector, true) == 0;
+}
diff --git a/gcc/omp-general.cc b/gcc/omp-general.cc
index 05b960e..c044d80 100644
--- a/gcc/omp-general.cc
+++ b/gcc/omp-general.cc
@@ -1271,8 +1271,9 @@ omp_context_name_list_prop (tree prop)
 }
 
 #define DELAY_METADIRECTIVES_AFTER_LTO { \
-  if (metadirective_p && !(cfun->curr_properties & PROP_gimple_lomp_dev))	\
-    return -1;	\
+  if (metadirective_p \
+      && !(cfun && cfun->curr_properties & PROP_gimple_lomp_dev)) \
+    return -1; \
 }
 
 /* Return 1 if context selector matches the current OpenMP context, 0
diff --git a/gcc/testsuite/ChangeLog.omp b/gcc/testsuite/ChangeLog.omp
index 162cbc5..2fc0f1d 100644
--- a/gcc/testsuite/ChangeLog.omp
+++ b/gcc/testsuite/ChangeLog.omp
@@ -1,3 +1,7 @@
+2022-02-11  Kwok Cheung Yeung  <kcy@codesourcery.com>
+
+	* gfortran.dg/gomp/metadirective-8.f90: New.
+
 2022-01-28  Kwok Cheung Yeung  <kcy@codesourcery.com>
 
 	* c-c++-common/gomp/metadirective-4.c (main): Add expected warning.
diff --git a/gcc/testsuite/gfortran.dg/gomp/metadirective-8.f90 b/gcc/testsuite/gfortran.dg/gomp/metadirective-8.f90
new file mode 100644
index 0000000..e134791
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/gomp/metadirective-8.f90
@@ -0,0 +1,22 @@
+! { dg-do compile }
+! { dg-additional-options "-fdump-tree-original" }
+
+program test
+  integer :: i
+  integer, parameter :: N = 100
+  integer :: sum = 0
+  
+  ! The compiler should never consider a situation where both metadirectives
+  ! match.  If it does, then the nested metadirective would be an error
+  ! as it is not a loop-nest as per the OpenMP specification.
+
+  !$omp metadirective when (implementation={vendor("ibm")}: &
+  !$omp&  target teams distribute)
+    !$omp metadirective when (implementation={vendor("gnu")}: parallel do)
+      do i = 1, N
+	sum = sum + i
+      end do
+end program
+
+! { dg-final { scan-tree-dump-not "when \\(implementation vendor \"ibm\"\\):" "original" } }
+! { dg-final { scan-tree-dump-times "when \\(implementation vendor \"gnu\"\\):" 1 "original" } }